Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$117.87	9.366%	$128.9097	$128.91	$128.90	$128.90
Purchase #2	$192.56	9.610%	$211.065	$211.07	$211.05	$211.10
Purchase #3	$196.81	8.137%	$212.8244	$212.82	$212.80	$212.80
Purchase #4	$141.52	12.283%	$158.9029	$158.90	$158.90	$158.90
Purchase #5	$250.59	10.107%	$275.9171	$275.92	$275.90	$275.90
Purchase #6	$52.73	12.758%	$59.4573	$59.46	$59.45	$59.50
Purchase #7	$177.60	11.613%	$198.2247	$198.22	$198.20	$198.20
7 purchase totals =	$1,129.68		$1,245.3011	$1,245.30	$1,245.20	$1,245.30